Staphylococcus pseudintermedius is a bacterium commonly found on dogs, often residing harmlessly on their skin and mucous membranes. While it is a normal part of a dog’s microflora, this bacterium can become problematic under certain conditions. Its transition to causing disease is contingent on other factors affecting the dog’s health or skin barrier.
Understanding Staphylococcus pseudintermedius
Staphylococcus pseudintermedius is a type of bacteria frequently found on the skin, nose, mouth, and even in the gastrointestinal tract of dogs. It is recognized as the most common species of bacteria present in dogs, colonizing a high percentage of healthy animals. This bacterium is considered an opportunistic pathogen, meaning it typically only causes issues when the dog’s skin barrier is compromised or its immune system is weakened. The highest prevalence is noted around the perineum, followed by the nasal or oral mucosa.
Infections Caused by Staphylococcus pseudintermedius
Staphylococcus pseudintermedius is a frequent cause of various infections in dogs, particularly those affecting the skin and ears. The most common skin infection is pyoderma, which involves a bacterial infection of the skin. This condition often manifests as redness, itching, pustules, hair loss, and sometimes an unpleasant odor. Superficial pyoderma, also known as superficial bacterial folliculitis, is a common presentation.
Beyond skin infections, S. pseudintermedius is also a common culprit in ear infections, specifically otitis externa. Symptoms of otitis externa can include redness of the ear, itching, head shaking, purulent discharge, swelling, and pain. These infections are frequently secondary to underlying issues, such as allergies, hormonal imbalances, or parasites.
Diagnosis and Treatment Approaches
Veterinarians typically diagnose Staphylococcus pseudintermedius infections using a combination of methods. Cytology, which involves examining skin samples under a microscope, is often the first step to identify the presence of bacteria and inflammatory cells. This quick, in-house test can confirm a bacterial cause and help differentiate pyoderma from other skin conditions.
For a more definitive diagnosis and to guide treatment, bacterial culture with antibiotic susceptibility testing, often referred to as C&S testing, is performed. This test identifies the specific bacterial species and determines which antibiotics will be effective against it. C&S testing is especially important due to the increasing prevalence of methicillin-resistant Staphylococcus pseudintermedius (MRSP), a strain that is resistant to common antibiotics like penicillins and cephalosporins.
Treatment approaches often combine topical therapies, such as shampoos containing 2% to 4% chlorhexidine or ointments with ingredients like fusidic acid or mupirocin, with systemic antibiotics. Topical treatments are beneficial as they remove bacteria-laden crusts, soothe the skin, and can reduce the duration of systemic antibiotic use, potentially limiting the development of resistance. Systemic antibiotics, like amoxicillin-clavulanate, cephalexin, or clindamycin, are prescribed based on susceptibility test results. It is important to complete the entire course of antibiotics, even if symptoms improve, to help prevent the development of antibiotic resistance.
Managing and Preventing Recurrences
Preventing recurrent Staphylococcus pseudintermedius infections in dogs largely depends on identifying and addressing the underlying causes. These can include allergies, hormonal imbalances like hypothyroidism, or parasitic infestations. Without managing these primary issues, the infections are likely to return, necessitating repeated treatments.
Ongoing skin hygiene plays a role in long-term management. Regular bathing with antiseptic shampoos, particularly those containing chlorhexidine, can help control bacterial populations on the skin and support skin barrier health. For localized areas, topical ointments can also be effective. Regular veterinary check-ups allow for early detection of potential issues and adjustments to management strategies, promoting sustained skin health and reducing the likelihood of infection recurrence.